Frame Structure : Some definitions
Container :
Basic package unit for PDH signal
Path Over Head :
Information added to manage the associated container
Virtual Container :
A container with an Over Head for alarms. performance and management
Pointer :
Localization of the VC in the STM payload
Tributary Unit :
A transport unit where are mapped the VC12 or VC3
Tributary Unit Group :
Collection of several TUs
Administrative Unit :
A transport unit where are mapped the VC4
Administrative Unit Group :
Multiplexing of several AUs
14
SDH TRAINING
14
.

Pseudo-synchronous mode
A mode where all clocks have a long-term frequency accuracy compliant with a primary reference clock as specified in Recommendation G.
Synchronous network
A network where all clocks have the same long-term accuracy under normal operating conditions
49
SDH TRAINING
49
. Not all clocks in the network will have timing traceable to the same PRC.Synchronisation : Definitions
Asynchronous mode
A mode where clocks are intended to operate in free running mode.
Master slave mode
A mode where a designated master clock is used as a frequency standard which is disseminated to all other clocks which are slaved to the master clock.811 under normal operating conditions.

The output is bounded to the input.811
NE is synchronized to an external source.811 G.
x Free Running : The Hold over mode is used up
SET
The NE provides its own clock.812
The data stored during locked mode is used to control phase and frequency variation.
x Hold Over : Takes place when external sources are no longer available
G.812 G.Synchronisation : NE Synchronisation mode
x Locked : Normal mode
G.
SET
50 SDH TRAINING 50
.